The effect of seeding on the microstructure and mechanical properties of hot-pressed silicon nitride was investigated by introducing large, elongated beta-Si3N4 particles into an alpha-Si3N4 matrix. Densification and fracture toughness were followed in the presence Of Y2O3 as sintering aid. The concentration of seeds varied from 0 to 5 wt%. The maximum fracture toughness was 8.0 MPam(1/2) for a material with 3 wt% seeds, hot pressed at 1750 degrees C, for 4h.